1. Field of the Invention
The present invention relates to tow trucks, particularly to an improved boom for such trucks.
2. Prior Art
A variety of tow trucks are known for towing disabled vehicles such as passenger cars or trucks. Specialized tow trucks are commercially popular. Multi-purpose flat bed trucks, which may be adapted for temporary towing purposes, are also known.
Specialized towing trucks are those which have generally met with the most commercial success. The specialized trucks normally include an overhead boom from which depends a sling or cradle attachable to the stalled vehicle for lifting and towing thereof. Stability of the lifted load is aided by a tow bar which extends rearwardly of the tow truck frame and which defines a fixed minimum distance of the lifted load from the tow truck.
The sling lifted tow trucks have been very popular in this country; however, attachment of the tow bar and sling to the vehicle frame or suspension is a dirty task, and as the lifting point of the disabled vehicle is near its front or rear bumper, damage such as denting or twisting to vehicle components is a frequent occurrence. Such damage has been increasing as more plastic parts and shock-collapsible bumpers have been incorporated into passenger cars.
Those tow trucks which utilize a cradle usually attach to the front or rear wheels of the vehicle to be towed. However, where the lifting point is about the wheels of the load (a wheel-lift), the tow truck carries a much higher portion of the towed vehicle's weight than when the lifting point is adjacent the towed vehicle bumper. Thus, although the wheel-lift tow trucks provide relatively clean attachment and greatly reduce the chances of damage to the towed vehicle, instability of the towed load in transit during acceleration and deceleration and instability of the towing truck due to longitudinal tire load transfer have been problems.
Among the multi-purpose flat bed trucks adapted for towing purposes are those disclosed by U.S. Pat. Nos. 4,000,823 and 3,908,842. The structure taught by these patents include the potential for damage to the towed vehicle similar to that of the commercial sling tow trucks, are not suitable for heavy duty towing, or incur stability problems in transit.